One of the most common errors in development is where a loop or a retrieval by index falls short or long by one unit, usually because of an oversight or a logic in coding.

Of the following snippets, which one will run 10 times?

/* #1 */    for (N = 0 ; N < 10; N++) printf("%d\n", N);

/* #2 */    for (N = 0 ; N <= 10; N++) printf("%d\n", N); 

/* #3 */    for (N = 1 ; N <= 10; N++) printf("%d\n", N);

/* #4 */    for (N = 1 ; N < 10; N++) printf("%d\n", N);

The question is deceptive, as there are two snippets that will run 10 times (1 and 3). But they will print different numbers. If you ware aiming for numbers from 1 to 10, only #3 is good.

After many years of programming, off-by-one errors are rare in my code, and I have been able to spot them or prevent them at first sight. That’s why I feel uneasy when I look at the way parallel replication is enabled in …

The new Continuent Tungsten 2.0.1 is now available. Continuent Tungsten 2.0.1 is the first generally available release of Continuent Tungsten 2.0, which offers major improvements to Continuent's industry-leading database-as-a-service offering. 

New features:

Replication

Provides low-impact, real-time replication with up-to 5X throughput over native MySQL and over 100X reduction in

MySQL Connector/Java has long had support for replication-aware deployment, allowing a single logical Connection object to effectively “pool” connections to both a master and (potentially multiple) slaves.  This allowed scale-out of read load by distribution of read traffic to slaves, while routing write load to the master.  The JDBC specification provides a nice hook to know what’s read-only traffic – Connection.setReadOnly().  When a boolean value of true is passed, a ReplicationConnection will route further commands a selected slave instance, while values of false trigger routing to the master.  This is sufficient for many simple replication topographies, but not all – most notably, it …

MySQL Fabric is a very promising sharding framework. If I take Ulf Wendel definition of MySQL Fabric :

MySQL Fabric is an administration tool to build large “farms” of MySQL servers. In its most basic form, a farm is a collection of MySQL Replication clusters. In its most advanced form, a farm is a collection of [...]

I want to thank all attendees of my webinar, “MySQL 5.6 New Replication Features: Benefits, Challenges and Limitations“. We had questions that I didn’t have the time to answer:

Q: If I run on Amazon’s RDS, do I need to worry about enabling crash-safe slaves, or is that already in place?

A: Crash-safe replication is already configured for read replicas using MySQL 5.6.

Q: How the relay log purge will manage in case of multiple db’s replication running on multiple threads?

A: Same thing as with single-threaded replication: when all event in a relay log file have been executed, …

As you might have noticed, we have released a framework for managing farms (or grids, as Justin suggested) of MySQL servers called MySQL Fabric. MySQL Fabric is focused on being easy to use and extensible, and two extensions are currently part of the framework: one to manage high-availability and one to implement sharding.

High-Availability Groups One of the central concepts used to construct a farm is the high-availability group (or just group when there is no risk of confusion) and is introduced by the high-availability extension. As mentioned in the previous post, the group concept does not really represent anything new but is rather a formalization of how we think and work with the structure of the …

On Wednesday I’ll be leading a webinar exploring MySQL 5.6’s new replication features. And yes, as usual I’ll deliver news on the good, the bad and the ugly (that is to say the benefits, limitations and challenges).

The webinar, appropriately titled, “New Replication Features in MySQL 5.6: Benefits, Limitations, and Challenges“, is scheduled for Oct. 23 at 10 a.m. Pacific Daylight Time. You can register now to reserve your spot (this webinar will also be available for playback afterward).

This session aims at exploring some of these …

Checking throughput with async MySQL replication

Replication throughput is the measure of just how fast the slaves can apply replication (at least by my definition).  In MySQL async replication this is important to know because the single-threaded apply nature of async replication can be a write performance bottleneck.  In a production system, we can tell how fast the slave is currently running (applying writes), and we might have historical data to check for the most throughput ever seen, but that doesn’t give us a solid way of determining where we stand right NOW().

An old consulting trick to answer this question is to simply stop replicating on your slave for a minute, (usually just the SQL_THREAD), restart it and watch how long it takes to catch up.  We can also watch the slave thread apply rate during this interval to get a sense of just how many writes per second we can do and compare that with the normal rate …

It's no secret that you shouldn't rely on replication filtering. Recently a customer asked if an `ON DELETE CASCADE` would still affect the data on a slave if the table was being ignored through replication filtering. It was one of those occasions that I couldn't give a confident answer without a quick test but alas the gut was right and the obvious answer is yes, "ON DELETE|UPDATE CASCADE" will change data even if you replicate using replication filters.

I tested using RBR and SBR. If anything I was questioning the behaviour of RBR here but it turns out to be consistent with SBR. I had a master-slave setup already deployed for some other testing so it was easy to implement the FKs needed for this. The dataset is the trusty world db available from dev.mysql.com and I needed to change the constraints on the table to match the conditions proposed.
Master …

MySQL Server 5.6 has seen fast adoption - the list of performance improvements and features make a convincing argument all on their own.

Join those adopting the MySQL database by taking the MySQL for Database Administrators training course.

This 5-day course teaches you all the core dba skills including what MySQL Server 5.6 brings you in terms of Replication. You will learn about:

• Managing the MySQL Binary Log
• MySQL replication threads and files
• Using MySQL Utilities for Replication
• Designing Complex Replication Topologies
• Multi-Master and Circular Replication
…